The invention relates to magnetic disk drives and particularly of the type adapted to accommodate disk-jacket assemblies. More particularly, the invention relates to mechanism for draining off accumulations of static electricity carried by the jacket and the disk of such an assembly.
Such disk-jacket assemblies have been previously proposed and are in current use. Such an assembly is described in the U.S. Pat. No. 3,668,658 issued June 6, 1972 to Ralph Flores et al. The assembly disclosed in this patent includes a magnetic disk which is contained and is rotatably disposed within a square jacket or cover. The jacket has a central opening for revealing a smaller central opening in the disk by means of which the disk can be driven, and the jacket contains two aligned radially extending slots through which a magnetic transducer may extend for the purpose of magnetically reading from or writing on a surface of the disk as the disk is rotatably driven.
High electrical resistance materials, such as polyvinyl chloride acetate, have been found particularly suitable for forming the jackets in such assemblies. The favorable characteristics of jackets formed with such materials are low-cost, resistance to impact, heat sealability for attaching parts of the jackets together to form a complete unit, etc.; however, jackets of such material have been found to accumulate static electricity due to normal handling. The disks in such assemblies are generally polyethylene terephthalate, also an insulator of high resistivity; and the static electricity also accumulates on the surfaces of the disks. Such accumulations of static electricity would provide spurious signals in transducers used with the disks as the static discharges; however, if the transducers are of an electrically conducting type, having their cores formed of iron, for example, these accumulations of static electricity are rapidly bled off so that they cause no trouble in ordinary usage of the disk-jacket assemblies. However, it has recently been found very advantageous to use magnetic transducers which are made completely of electrical insulating material. Such a transducer is disclosed in U.S. Pat. No. 3,846,840 issued Nov. 5, 1974 and includes ferrite cores having the transducing gaps therein and having windings disposed therein for reading, writing or erasing information on the associated disk. Such a transducer also includes outriggers attached to the ferrite cores which are composed of ceramic material. The outriggers are used on the opposite sides of the cores for increasing the surface of the transducer that makes contact or has a close air bearing with the disk. Both the ferrite and the ceramic material are of electrically insulating nature and retard the bleeding off of the accumulated static charge on the jacket and magnetic disk for a very substantial time, such as 15 or 20 minutes. The disk drive thus is rendered incapacitated and unusable for this extended period of time.